Switching crosspoint arrangment



Sept. 30, 1969 A. H. BOBECK 3 7 SWITCHING CROSSPOIN'I' ARRANGEMENT IFiled Sept. 16, 1966 I 3 Sheets-Sheet l CONTROL CIRCUIT ADDRESSEDCIRCUITS PROPAGATION CIRCUIT /N VENT OR ,4. 11.. BOBECK A TTORNE I"Sept. 30, 1969 A. H. BO BECK SWITCHING CROSSPOINT ARRANGEMENT 3Sheets-Sheet 2 Filed Sept. 16. 1966 FIG. 3

Sept. 30, 1969 A. H. BOBECK 3,470,547

SWITCHING CROSSPOINT ARRANGEMENT Filed Sept. 16, 1966 3 Sheets-Sheet 3United States Patent 3,470,547 SWETCHINQ CRDSSPQENT ARRANGEMENT AndrewH. Boheck, Chatham, Null, assignor to Bell Telephone Laboratories,Incorporated, Murray Hill and Berkeley Heights, N.J., a corporation ofNew York Filed Sept. 16, 1966, Ser. No. 579,905 Int. U. H0111 63/33 US.Cl. 34tl174 9 Claims ABSTRACT 0F THE DISCLOSURE A selected one of amatrix of crosspoints defined by X and Y oriented conductors can beclosed by pinching the Wires together at the selected location. Themovement of a magnetic domain associated with a Y conductor at eachcrosspoint controls the attraction of a magnet associated with the Xconductor at each crosspoint.

This invention relates to switching system networks and, moreparticularly, to such networks including switching crosspoints.

Switching system networks have at their very heart crosspoint switcheswhich are selectively closed for providing a speaking path betweenassociated X and Y channels. Considerable effort has been expended tofind ever better and ever cheaper crosspoints, an effort realized to bejustified when one appreciates the extent to which such crosspoints areused. Even a small improvement in operating characteristics or a modestreduction in cost is eagerly sought after. 7

The reed switch is one type of crosspoint switch which is now widelyused. The reed switch is an electromechanical device including normallyspaced apart cantilevered contacts which close under the influence of amagnetic field to provide the requisite connection between coordinatechannels when selected. The contacts in a reed switch are (resilient or)spring loaded for returning the contacts to the open condition whenreleased. The spring, of course, presents an additional load which is tobe overcome when a selected crosspoint is to be closed. Consequently,the pull required to close a reed switch at a selected crosspoint isgreater than would be required in the absence of such a spring thusnecessitating a relatively high drive. In addition, the entirecantilevered contact structure of a reed switch provides an extendedclosure path of limited cross section through which flux is provided foreffecting the closed condition. The losses associated with the contactstructure further increase the requisite drive.

It is an object of this invention to provide a new and r novelcrosspoint matrix having relatively low drive requirements.

The invention, in one aspect thereof, is based on the realization that asingle wail (reverse) domain in a'magnetic sheet provides suificientflux in a direction normal to the plane of the sheet to close a contactof the type described. Such a magnetic sheet is also characterized inthat the absence of a single wall domain in a particular locationprovides flux of an equal and opposite polarity for repelling thecontact. Single wall domains and the movement thereof selectively intransverse directions in a magnetic sheet are described in copendingapplication Ser. No. 579,995, filed Sept. 16, 1966, for P. C. Michaelisand in copending application Ser. No. 579,931, filed Sept. 16, 1966, forA. H. Bobeck, U. P. Gianola, R. C. Sherwood, and W. Shockley. The formerapplication describes the storage and movement of such single walldomains in magnetic films with preferred magnetization directions in theplane of the magnetic film. The latter describes the storage andmovement of single wall domains in a sheet Patented Sept. 30, 1969 ICCof magnetic material with a preferred magnetization direction normal tothe plane of the sheet. Either arrangement is useful in accordance withthe teachings of this invention.

Briefly, in accordance with one aspect of this invention, a matrix oftwo-position (1 and 0) bit locations is defined in a sheet of magneticmaterial substantially isotropic in the plane of the sheet and having apreferred magnetization direction illustratively normal to the plane ofthe sheet. A single wall domain is stored in the 0 position of each bitlocation and a permanent magnet is associated with each 1 position. Xconductors are associated with rows of permanent magnets; Y conductorsare associated with columns of bit locations. When a single wall domainis moved from a 0 to a 1 position in a selected bit location, itattracts the associated permanent magnet placing the corresponding X andY conductors in contact there. In the absence of such a selection, arepelling force is present at the 1 position maintaining thecorresponding permanent magnet at a distance avoiding a connection atthat crosspoint.

In accordance with another aspect of this invention, reverse domainshaving leading and trailing domain walls are expanded selectively fromfirst to second positions in bit locations in domain wall wires forsimilarly making connections at crosspoints.

A feature of this invention is a switching network crosspoint matrixincluding a magnetic medium, means defining a matrix of two-position bitlocations in the medium, the first position in each bit locationincluding a reverse magnetized domain, means selectively movingmagnetized domains to second positions in corresponding bit locations,magnet means associated with each second position and X and Y conductorsassociated with the magnet means and the magnetic medium respectively.

The foregoing and further objects and features of this invention will beunderstood more fully from a consideration of the following detaileddiscussion rendered in conjunction with the accompanying drawingwherein:

FIG. 1 is an exploded schematic view of a crosspoint matrix inaccordance with this invention;

FIGS. 2, 3, 4, 5, 6, and 7 are schematic views of portions of the matrixof FIG. 1; and

FIGS. 8, 9, and 10 are schematic views of portions of another crosspointmatrix in accordance with this invention.

FIG. 1 shows a crosspoint matrix 10 in accordance with one aspect ofthis invention. The crosspoint matrix is composed of first, second, andthird planar portions 11, 12, and 13 juxtaposed with one another. Planarportion 11 comprises, illustratively, a sheet of yttrium orthoferrite 15with spaced apart Y conductors Y1, Y2, and Y3 thereon. The Y. conductorsare connected to individual circuits such as, for example, telephonesubsets represented collectively as block 16 designated addressedcircuits. Such interconnections are well understood in the art and adiscussion thereof is not necessary for an understanding of thisinvention.

Planar portion 11 also includes propagation conductors represented inFIG. 1 by conductor indications 17 and 18 in FIG. 1 and described indetail in connection with FIG. 2. Conductor indications 17 and 18 areconnected to a propagation circuit represented by a block 19, sodesignated, in FIG. 1 and also discussed further in connection with FIG.2. For the present it is assumed that the propagation circuit defines amatrix of two-position bit locations in the orthoferrite sheet. Thiswill become clear in the discussion of that circuit in connection withFIG. 2 hereinafter. It is further assumed that one position in each ofthese locations is occupied by a single wall domain. Such domains areprovided in those positions by means disclosed, for example, in theaforementioned application of A. H. Bobeck et al. It is contemplated toprepare the orthoferrite sheet initially with the domains disposed asrequired. Consequently, input circuitry and the means for so disposingthe domains are not required for continued operation of a crosspointmatrix in accordance with the teachings of this invention. Nor is adiscussion of such implementations necessary for an understanding of theinvention. It is suflicient to call for the presence of such domains,provided by means disclosed elsewhere and to state that the function ofthe propagation circuit is to move a selected domain from a first to asecond position and back again on a random access basis. The specificoperation of the propagation circuit to this end will be discussed afterthe discussion of the structure of FIG. 1 is completed.

Planar portion 12 of crosspoint matrix is an apertured plastic filmwhich overlies sheet 11.

Planar portion 13 comprises a weave of a plastic warp with respect towhich electrically conducting wires X1 and X2 comprise the woof.Conductors X1 and X2 are connected to block 20, designated originatingcircuit in FIG. 1. Block may also represent a plurality of telephonesubsets as is well understood in the art.

Permanent magnets positioned at what is conveniently designated bitlocations BL11, BL12 BL21 and BL23, as will become clear, are aflixed tocrosspoints defined by the intersections of the warp and the woof ofplanar portion 13. Each magnet is positioned to correspond to the secondposition of a bit location in the orthoferrite sheet. Each magnet ispositioned also to correspond to apertures in the plastic film of planarportion 12 in order to pass therethrough when attracted by the flux of asingle wall domain when the latter is moved to a second position in aselected bit location.

The originating, addressed, and propagation circuits 20, 16, and 19 areconnected to a control circuit 22 by means of conductors 23, 24, and 25,respectively. The various circuits may be any such circuits capable ofoperating in accordance with this invention. In the context of atelephone system, the control circuit may comprise central otficeswitching equipment. The originating and addressed circuits may comprisetelephone subsets as already stated.

FIG. 2 shows the propagation circuit represented by conductorindications 17 and 18 and block 19 in FIG. 1. The circuit is arrangedillustratively for six bits. It is clear that the indications 17 and 18of FIG. 1 represent a plurality of rows and columns of drive conductors.Specifically, the propagation circuit comprises a plurality of rowconductors PX1, PX2, PX3, and PX4. Each of those conductors has a returnpath to ground and forms with corresponding portions of its return pathcircular conducting loops in rows as shown. A single wall domain isstored initially in the magnetic sheet at positions defined by theconducting loops formed by conductors PX2 and PX4 and their respectivereturn paths. The conductors PX1, PX2, PX3, and PX4 originate at an X.driver 30.

Similarly, the propagation circuit also comprises a plurality of columnconductors PYl, PY2, PY3, and PY6. Each of these conductors also has areturn path to ground and forms conducting loops therewith. The loops soformed are arranged in columns providing, with corresponding loopsformed by conductors PX1, PX2, PX3, and PX4 with the respective returnpaths, a set of four loops oriented illustratively along a diagonal ateach bit location as viewed in FIG. 2. The four loops in each bitlocation are next adjacent one another in practice but are shown spacedapart for convenience in the figure. The conductors PYl PY6 originate ata Y driver 31.

The conducting loops formed by conductors PY2, PY4, and PY6 are shownblackened in FIG. 2. The magnets associated with bit locations BL11 andBL23 shown in FIG. 1 are positioned in planar portion 13 to 4 correspondto those blackened loops. The object of the propagation circuit then isto move the single wall domain from the position in which it isinitially stored to the position of the corresponding blackened loop ina selected .bit location.

Let us assume that the entire sheet of magnetic material is in amagnetic condition where flux is directed downward into the plane of thesheet as represented by the minus signs in FIG. 1. The single walldomains stored in first positions in the bit locations then may berepresented by plus signs at those first positions. The domain wall ofthe single wall domain may be thought of as corresponding in position tothe conducting loop thereabout. Actually single wall domains may extendbeyond the confines of the conducting loop as described in theaforementioned Bobeck et al. application.

A positive pulse, applied by driver 30 to conductor PX1 under thecontrol of control circuit 22, generates a propagation field for movingthe single wall domain in each bit location therealong to the positionof the conducting loop defined thereby in the corresponding bitlocation. FIG. 3 shows an abstraction representing the conducting loopsshown in FIG. 2. When conductor PX1 is pulsed, the single wall domainsin bit locations in the magnetic sheet coupled thereby are moved topositions then as shown in FIG. 3.

Next a negative (for the sense shown) pulse is provided similarly onconductor PYl. The single wall domain in location BL11 is now in alocation defined by the corresponding conducting loop in conductor PYl.The remaining domains in hit location BL12 associated with thatconductor are not moved in response to the pulse on conductor PYl. Thedisposition of domains is as shown in FIG. 4.

Thereafter a negative pulse is applied similarly to conductor PY2, alsounder the control of control circuit 22, moving the domain in bitlocation BL11 to the position of the blackened loop there. Thedisposition of domains is as shown in FIG. 5. It is clear that only thesingle wall domain in bit location BL11 is in a (second) positioncorresponding to the position of a permanent magnet in planar portion 13of FIG. 1.

When the single wall domain is in the initial position, conductors X1and Y1 are spaced apart as shown in FIG. 6. When the single wall domainis moved to the second (blackened) position in selected bit locationBL11, the permanent magnet in that bit location is pulled toward sheet15 for placing conductor X1 in contact with conductor Y1 there as shownin FIG. 7. The plastic film of planar portion 12 is to insure that nextadjacent magnets are not affected by the movement of a selected magnet.

Finally, a positive pulse is applied similarly to conductor PX2 forreturning domains in disturbed zero positions, as shown in bit locationsBL12 and BL13 in FIG. 5, to initial positions.

The single wall domain is returned to its initial position selectivelyfrom the one position as shown in bit location BL11 in FIG. 5 by asimilar propagation pulse sequence on conductors PYI, PX1, PX2, andfinally on conductor PY2, the latter pulse being applied to return toone position domains in any previously selected locations disturbed bythe present selection. All pulses are applied by drivers 30 and 31 underthe control of control circuit 22.

A four pulse selection sequence is applied in microseconds. The wiresrequire milliseconds to come into contact or to move apart. Accordingly,the disturb effects are negligible. The propagation operation isentirely consistent with that described in copending application Ser.No. 579,904, filed Sept. 16, 1966, for A. H. Bobeck.

A recitation of the dimensions and operating parameters for a crosspointmatrix as shown in FIG. 1 emphasizes the advantages of such anarrangement. The magnetic sheet 15 is about one inch by one inch bythirty mils thick. A single wall domain has a diameter of about fiftymils. The plastic film of planar portion 12 is typically two mils thick,corresponding to the normal spacing between X and Y conductors. Eachpermanent magnet has a diameter approximately equal to that of a singlewall domain and is about thirty mils thick. The permanent magnets shownin FIG. 1 are magnetized such that the flux is directed downwardtherefrom as viewed in the figure. The X and Y conductors havecross-sectional areas of about two square mils suflicient to carrycurrents common for such circuits. A suitable attracting force of morethan one gram is easily provided by a single wall domain. A repellingforce of comparable magnitude is present in the absence of a single walldomain. A single wall domain is moved in available magnetic sheets byabout one oersted fields provided with drive currents of the order ofone ampere (through a single turn) and switching speeds on the order ofmicroseconds are realized. This is to be compared with currents of aboutten amperes required by a reed switch having, typically, on the order oftwenty turns. It is clear that the matrix of FIG. 1 not only is of aconvenient size and amenable to mass fabrication techniques but alsopermits a reduction of over an order of magnitude in drive requirements(on an ampere turn basis) over prior art circuitry operating in similarfashion.

Planar portion 11 of FIG. 1 may, alternatively, be formed by a pluralityof domain wall wires which conveniently are electrically conductingalso. FIG. 8 depicts a portion of such a planar wire counterpart of theembodiment of FIGS. 1 and 2 showing only a portion of the propagationcircuitry therefor. Specifically, FIG. 8 shows portions of first andsecond electrically conducting domain wall wires DW1 and DW2 shownconnected to an addressed circuit as represented by block 16 of FIG. 1(only indicated here). A reverse domain is represented in a domain wallwire by an arrow directed to the right as viewed and bounded by verticallines representing leading and trailing domain walls. The reversedomains are stored initially at positions corresponding to the left edgeof conductors PXZ and PX4. The wires are otherwise in an initializedmagnetic state represented by arrows directed to the left as viewed.

A plurality of propagation conductors PX1 PX4, and PY1 PY4, designatedto correspond to their counterparts in the embodiment of FIG. 1 couplenext adjacent portions of wires DW1 and DW2 to provide a uniqueexpansion of only a selected reverse domain from an initial firstposition to a second position corresponding to the position indicated bythe blackened reverse domain symbol as shown at bit location BLll inFIG. 8. To this end, a sequence of pulses on conductors PXZ, PY1, PY2,and (a negative pulse)PX2 expands a reverse domain uniquely from aninitial (first) position in bit location -BL11 to encompass the secondposition there by the provision of step-along fields in coupled portionsof the wire. Only in the bit location where the first three pulses ofthe propagation sequence are applied is a domain expanded to the secondposition. The last-mentioned pulse corrects disturbed information innonselected locations as described hereinbefore. A sequence of negativepulses PY2, -PY1, -PX2, and positive pulses +PY1 and +PY2 similarlyselectively returns the domain to the initial condition. It should beclear that the X1 conductor shown in the embodiment of FIGS. 1 and 2 isnot necessary in the embodiment of FIG. 8 and may be omitted oralternatively used for some other purposes, such as for nucleatingreverse domains initially. The organization of the propagation circuitryis entirely analogous to that shown in FIG. 2.

A more complicated propagation scheme permits movement of a domain in awire rather than the expansion of the domain as described, care beingtaken to advance the trailing wall of the domain synchronously.

Corresponding permanent magnets as shown in FIG. 1 are again positionedto correspond to second positions for cooperating with the embodiment ofFIG. 8. Thus closure of the selected crosspoint is elfected and atalking path is established between conductor X1 of FIG. 1 and domainwall wire DW1 which may function also as conductor Y1 of FIG. 1 in thisembodiment.

FIGS. 9 and 10 illustrate the attract and repel conditions in theoperation of a representative bit location in the embodiment of FIG. 8.The permanent magnet PM in this embodiment is assumed magnetized asindicated by the arrow directed to the left there as viewed. The reversedomain is shown in FIG. 9 expanded to the second position in bitlocation BLll. As is indicated by the plus and minus signs in thefigure, the reverse domain and the permanent magnet are poled inopposite directions providing the force of attraction bringing conductorX1 and conducting magnetic wire DW1 in contact there. The force ofattraction is indicated by the downward directed arrows in FIG. 9.

FIG. 10 shows the domain in the first position of bit location BLll. Thepositive poles of the permanent magnet and the domain are positionedopposite one another and thus provide a repelling force indicated by theupward directed arrows in the figure.

The domain wall wire, typically, has a diameter of seven mils andcomprises a material having a coercive force of about five oersteds toprovide sufiicient flux for insuring operation as desribed. Domains insuch a wire are typically 500 mils long and the permanent magnets areconveniently 1500 mils to cooperate therewith.

If the permanent magnet PM of FIG. 9 is displaced to the left as viewedsuch that its negative end coincides with, for example, the PY1conductor rather than the PY2 conductor at bit location BL11, then theconductor PY2 may be omitted. Operation on a random access basis isstill provided.

What has been described is considered only illustrative of theprinciples of this invention. Accordingly, various and numerous otherarrangements may be devised by one skilled in the art without departingfrom the spirit and scope of this invention.

What is claimed is:

1. A combination comprising a plurality of X conductors, a plurality ofY conductors spaced apart from said X conductors and forming crosspointstherewith, a magnetic element associated with said X conductors at eachof said crosspoints, means defining a plurality of magnetic storagelocations having both first positions in cluding a reverse magnetizeddomain and second positions associated with said Y conductors at each ofsaid crosspoints, and means selectively moving said reverse magnetizeddomain from a first to a second position at a selected crosspoint forattracting the corresponding magnet thus making contact between theassociated X and Y conductors.

2. A combination in accordance with claim 1 wherein said memory meanscomprises a sheet of magnetic material substantially isotropic in theplane of the sheet and having a preferred magnetization directionsubstantially normal to the plane of the sheet, and said reverse domainsare single wall domains.

3. A combination in accordance with claim 1 wherein said memory meanscomprises a film of anisotropic material, and said reverse domains aresingle Wall domains.

4. A combination in accordance with claim 1 wherein said memory meanscomprises a plurality of domain wall wires and said reverse domains arebounded by leading and trailing domain walls.

5. A combination in accordance with claim 1 also including first circuitmeans connected to said X conductors and second circuit means connectedto said Y conductors, said contact between selected X and Y conductorsproviding a unique communication channel between said first and secondcircuit means.

6. A combination in accordance with claim 2 wherein said means defininga plurality of magnetic storage locations comprises a plurality of X andY conductors each including'a' return path and defining with corresponding portions of said return paths electrically conducting loops fordefining bit locations in said sheet, and circuit means selectivelyapplying pulses to said X and Y conductors.

7. A combination in accordance with claim 6 wherein said X and Yconductors are organized in pairs for defining in said sheet bitlocations including four of said conducting loops for providing a randomaccess organization wheren said first and second positions are spacedapart by first and second intermediate positions.

8. A combination in accordance with claim 2 Wherein said X conductorsand said Y conductors are arranged in planes spaced apart by anapertured insulating film.

9. A combination in accordance with claim4 wherein said meansselectively moving said reverse domain com prises means selectivelyexpanding said domain.

References Cited UNITED STATES PATENTS 3,268,840 8/ 1966 Hjertstrand335-4205 3,295,114 12/1966 Snyder 340--174 OTHER REFERENCES j Spain, R.1., Controlled Tip Propagation, Part I. Journal of Applied Physics, vol.37, No. 7, June 1966, pp.

15 User. XLR.

